1. Field of the Invention
The present invention relates to a heating apparatus for controlling, based on an accelerating state of a vehicle a rotation as well as a stop of the rotation of a rotor in a heat-generating unit using a shearing force, for heating cooling water to be supplied from an engine to a heating heat exchanger.
2. Description of Related Art
Conventionally, as a heating apparatus for a vehicle, there has been generally known a hot water type heating apparatus for heating a passenger compartment, in which cooling water for cooling a water-cooled engine is supplied to a heater core disposed in a ducts and air heated while passing through the heater core is blown into the passenger compartment by a blower to heat the passenger compartment.
Recently, an improvement of an engine efficiency is highly demanded for an engine mounted on a vehicle; however, when the engine efficiency improves, heat loss decreases; and therefore the cooling water for cooling the engine cannot be heated sufficiently. Further, in a case of a vehicle having a diesel engine or a lean burn engine, the heat amount generated by the engine is too small to heat the cooling water sufficiently. In the vehicle where the heat amount generated by the engine is small, a temperature of the cooling water in the cooling water circuit cannot be maintained at a predetermined temperature (e.g., 80.degree. C.), there occurs a problem in that a heating capacity for the passenger compartment is insufficient.
To overcome such a problem, as disclosed in JP-A-2-246823 or JP-A-3-57877, there has been conventionally proposed a heating apparatus for a vehicle, in which a heat-generating unit using a shearing force, for heating cooling water supplied from the engine to the heater core is disposed in a cooling water circuits and when a temperature of the cooling water in the cooling water circuit, detected by a cooling water temperature sensor, is lower than a set cooling water temperature, the heat-generating unit is operated to improve the heating capacity for the passenger compartment.
The heat-generating unit transmits a rotational driving force of the engine to a shaft through a belt transmitting mechanism and an electromagnetic clutch, a heat-generating chamber is formed in a housing, and a cooling water passage is formed at an outer periphery of the heat-generating chamber. Further, a rotor which rotates integrally with the shaft is disposed in the heat-generating chamber, and a shearing force generated by a rotation of the rotor is applied to viscous fluid such as silicon oil sealed in the heat-generating chamber to generate heat. The cooling water is heated by the generated heat. That is, the heating apparatus for a vehicle uses a rotational driving force (driving torque) applied to the rotor of the heat-generating unit as an auxiliary heat source for heating operation.
In the heating apparatus for a vehicle, provided with the conventional heat-generating unit, because a rotational driving force (driving torque) applied to the rotor of the heat-generating unit is used as the auxiliary heat source for heating operation, a large driving load is applied to the engine by the driving torque. Therefore, while the heat-generating unit is operating, if a driver desires an acceleration and steps on an acceleration pedal an accelerating state suitable for an intention of the driver cannot be obtained, because a driving load of the engine is increased. There occurs a problem that a driveability deteriorates or an emission (NOx) increases.